The present invention relates generally to methods and apparatus for coating articles, such as optical articles, such as but not limited to optical lenses.
Optical lenses, such as glass or plastic lenses for conventional eyeglasses, are in wide use today. A functional coating may be applied to the surface of these lenses to provide the lenses with certain desired properties, such as improved mar and scratch resistance, antireflection properties, or polarization properties, just to name a few. These coatings are typically applied using a spin coating technique in which a liquid coating material is deposited in the middle of the lens while the lens is spinning. Centrifugal force causes the coating material to spread out over the surface of the spinning lens. The lens is then stopped and the coating material cured, such as by heating or air-drying, to form a coated lens.
While adequate for most uses, this spin coating technique does have some drawbacks. For example, this spin coating technique may lead to non-uniform coating thickness across the lens surface, e.g., the coating applied by a spin coating technique may be thicker at the edges of the lens than in the middle of the lens due to centrifugal force directing the coating flow outwardly from the center of the lens to the edge of the lens. For functional coatings, this may lead to a difference in performance across the lens surface. Additionally, the spin coating technique is not well suited for coating multi-focal lenses. By “multi-focal lenses” is meant lenses having more than one focal prescription, such as conventional bifocal or trifocal lenses. In these multi-focal lenses, there is typically an edge between one focal prescription and the other focal prescription(s) such that the surface of the lens is uneven, i.e., not of uniform curvature or flatness across the lens surface. Spin coating may lead to pooling or disruption of the coating flow at these uneven surface regions. Moreover, conventional spin coaters are relatively complex in design because the holder in which the lenses are placed must be capable of rotating the lenses at a predetermined speed during the spin coating process. Additionally, the time required to start the lens spinning before coating and then to stop the lens after coating decreases the coating efficiency and throughput of the spin coater.
Therefore, it would be advantageous to provide a method and/or apparatus for coating articles, such as optical lenses, which eliminates or reduces at least some of the problems associated with conventional spin coating.